SLO to remove toxic dry cleaning chemicals from groundwater basin. Here’s how

San Luis Obispo sits atop a large groundwater basin — but chemicals swirling in the water prevent the city from using it for drinking.

The city won a $6.6 million grant to install wells that remove tetrachloroethylene, a colorless chemical also known as PCE, from the groundwater, according to city water resources program manager Nick Teague.

The wells should be operational by 2026 and will allow the city to fulfill 10% to 12% of its drinking water needs, he said.

The city presented the project at a meeting Tuesday evening at the San Luis Obispo City-County Library.

“The city is really excited about this project,” Teague said. “It’s not very often that you get to produce a new water source for the city.”

SLO groundwater contaminated with PCE

A section of the basin under San Luis Obispo contains about 57 gallons of PCE pollution, a toxic chemical formerly used by dry cleaners, according to Teague.

The largest amount of PCE is concentrated underneath Higuera and South streets. The plume extends southwest along Highway 101 to Los Osos Valley Road where a fault line blocks the pollution from spreading further.

PCE is heavier than water, so much of it settled into the bottom of the southern end of the basin, city water systems consulting program manager Josh Reynolds said.

The city stopped using the basin for drinking water during the 1990s, Teague said.

The Edna Valley side of the basin experiences an annual overdraft of about 1,100 acre-feet per year due to the high demand of agriculture, while the SLO side has a surplus of about 700 acre-feet of water per year, he said.

EPA banned use of toxic dry cleaning chemical

The Environmental Protection Agency banned most uses of two other similar dry-cleaning chemicals on Monday, according to a news release from the agency.

Those chemicals are perchloroethylene, also known as PCE, and trichloroethylene, known as TCE.

Decades of pollution from the chemicals by dry-cleaning businesses across the state was the subject of a three-part investigative series by former Tribune reporter Mackenzie Shuman in 2023.

Exposure to the chemicals can cause various cancers and damage the central nervous system, immune system and reproductive system.

Exclusive: How pollution from dry cleaners left California sitting on cancer-linked ‘time bombs’

Exclusive: California’s small dry cleaners face massive bills to clean up toxic chemical

Exclusive: How can California help clean up thousands of polluted dry cleaning sites?

TCE will be completely banned over time, while PCE will be allowed in workplaces “only where robust workplace controls can be implemented,” the release said.

“It’s simply unacceptable to continue to allow cancer-causing chemicals to be used for things like glue, dry cleaning or stain removers when safer alternatives exist,” the EPA’s Office of Chemical Safety and Pollution Prevention assistant administrator Michal Freedhoff said in the release. “These rules are grounded in the best-available science that demonstrates the harmful impacts of PCE and TCE.”

The ban won’t have much of an impact on the groundwater cleanup project, though, Teague said.

The city hasn’t identified any new sources of PCE pollution in the basin, so Teague thinks the pollution was caused by an operation that has since closed.

Still, he said he’s glad there will be no new opportunities for PCE to leak into the groundwater supply.

Grant funds pollution cleanup

The California State Water Resources Board awarded the city a $6.6 million grant to clean up PCE pollution in the basin earlier this year.

The grant will fund the construction of two wells that use a granular activated carbon system to remove PCE from the ground water — similar to how a Brita removes contaminants like lead, chlorine and mercury from tap water.

After filtration, the water will meet standards set by the California Division of Drinking Water and the Environmental Protection Agency.

Each well will have two filters, one that removes the PCE from the water and another that serves as a backup unit. The city will test the water between each filter and replace them as needed.

Meanwhile, the city will install about eight monitoring wells to evaluate water levels and the distribution of PCE in the basin, Reynolds said.

Eventually, this process will remove almost all PCE from the groundwater.

“Through this cleanup project, we can improve groundwater quality not just for the use of the city but within the basin in general,” Reynolds said.

The city’s water supply allows for the use of up to 10,183 acre feet of water per year, Teague said. However, the city only uses 5,250 acre feet of water annually, he said.

Right now, the city sources about 4,910 acre feet of drinking water per year from the Salinas and Whale Rock Reservoirs and 5,482 acre feet of water annually from the Nacimiento Reservoir, he said.

Recycled water accounts for about 5% of the city’s water supply, and is used to irrigate landscapes like parks and medians, he said.

This new project, however, will allow the city to pump about enough water to meet 10% to 12% of the city’s drinking water needs.

“We’re trying to increase our water resiliency,” Teague said.

Pumping and cleaning the groundwater will be cheaper and more energy efficient than cleaning surface water because groundwater experiences a natural filtration process. It also provides the city a backup plan if something happens to the reservoirs.

The city will monitor groundwater levels during the project to determine if they should reduce pumping.